Current measuring element with a hall sensor

ABSTRACT

A current measuring element comprising a current carrying conductor having the shape of a flat rail in an insulating housing and a hall sensor which is arranged in the proximity of said conductor. The current carrying conductor is bent to form a unshaped conductor loop in the area of the hall sensor and the hall sensor is situated on a board which is arranged in the unshaped conductor loop. The board containing the hall sensor is placed upon a main board on which the signal from the hall sensor is processed. An insulating cover provided for the housing is arranged between the housing containing the current carrying conductor and the main board. The cover comprises an insulating compartment which extends inside the conductor loop and receives the board containing the hall sensor.

TECHNICAL FIELD

The invention relates to a current measuring device having a currentcarrying conductor in an insulating housing and a Hall sensor arrangedin the vicinity of the conductor. Such a current measuring device isdescribed in EP 0 538 658 A1, for example.

BACKGROUND OF THE INVENTION

Hall sensors can be used to measure the current flowing in a conductorwithout making contact, as is known. To concentrate the magnetic fieldof the current, which is responsible for the Hall effect, and to excludeinterfering influences, it is general practice to use ferromagneticelements having a clearance which contains the Hall sensor.

In the current measuring device which is described in the aforementioneddocument EP 0 538 658 and can be used in power switches and motorprotective circuit breakers, the current flows through a coil which issplit into two halves and whose common coil former is provided with apocket for holding the integrated Hall circuit.

DE-A-34 28 392 discloses a similar current measuring device in which acurrent carrying conductor in the form of a coil or a bent railsurrounds a Hall sensor and is itself surrounded by a ferromagnetic coreto concentrate the magnetic field.

Such embodiments of the current measuring device with coils andferromagnetic cores and the like have the disadvantage that the coilsand cores make the structure very large and heavy.

DE-A-195 49 181 discloses a current measuring device in which a Hallsensor is inserted between the limbs of a U-shaped conductor loop,without a ferromagnetic core being connected in between. This measuringdevice has no shield, however, and is therefore relatively inaccurateand is not suitable for measuring heavy currents, at least.

SUMMARY OF THE INVENTION

The invention is based on the object of refining the current measuringdevice such that it is of simple design, is small and lightweight andcan thus be used universally.

The invention achieves this object with the features specified in patentclaim 1. Advantageous refinements of the current measuring deviceaccording to the invention are specified in the subclaims.

Dispensing with a coil and a ferromagnetic core or another ferromagneticelement not only simplifies the design of the current measuring device,but also means that significantly less heat is produced during operationon account of the fact that transfer losses no longer occur. This is ofconsiderable importance particularly for use in switchboxes.

The two current paths, carrying flow in opposite directions parallel toone another, in the U-shaped conductor loop comprising flat busbarscause the magnetic field, and hence the signal from the Hall sensor, tobe virtually doubled.

The current measuring device according to the invention for measuringcurrent without making contact is so small that it can easily beincorporated in measuring boxes and switching devices. The currentmeasuring device according to the invention already integrates theelectronics for amplifying and evaluating the measured signal, atemperature compensation means and possibly a control logic unit and adigital display.

The fully closed, insulating cover between the housing with the currentcarrying conductor and the circuit board with the Hall sensors and theevaluation electronics ensures complete DC isolation of the high-voltageregion from the electronic components.

The optionally provided metallic shield around the U-shaped conductorloop reduces the influence of interfering magnetic fields on the Hallsensor.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention's current measuring device with a Hall sensor is explainedin more detail below by way of example with the aid of the drawing, inwhich:

FIG. 1 shows the structure of the current measuring device,

FIG. 2 shows the circuit board with the Hall sensor in detail, and

FIG. 3 shows a block circuit diagram for signal processing in thecurrent measuring device.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows the structure of the current measuring device in anexploded view. The current measuring device comprises an insulatinghousing 10 for one or more current carrying conductors 12 in the form offlat rails of the type conventional in power engineering. The housing 10shown in FIG. 1 comprises three conductors 12 running in parallel forthe three-phase supply of current to a load, e.g. a motor.

The current measuring device shown is provided for use in thelow-voltage/heavy-current field with current levels of up toapproximately 150 A. The lowest current level which the measuring deviceis designed to record is between 0.1 and 1 A.

At the input and at the output of the housing 10, the conductors 12 areprovided with connection elements (not shown) so that each of theconductors 12 can be connected into the corresponding power supply line.The insulating covering, on the input side and the output side, for theconductors 12 and the connection elements is likewise not shown.

In the housing 10, each of the flat, rail-like conductors 12 is bent ina U shape so that a conductor loop 14 which is open at the top isproduced. The U-shaped conductor loop 14 extends downward out of theplane of the flat conductor 12, that is to say it is not situated in theplane of the flat conductor 12, but rather runs perpendicular to it. Ifthe width of the current conductor rail 12 is 12 mm, the conductor loop14 has, by way of example, a depth of approximately 15 mm and aninternal spacing between the limbs of the U of approximately 5 to 8 mm.

Each of the U-shaped conductor loops 14 can be surrounded on theoutside, that is to say in the region of the housing 10 below theconductor 12 and the conductor loop 14, by a metallic shield (not shown)which reduces or eliminates the influence of interfering externalmagnetic fields on current measurement. The shield is preferably made ofsoft iron (Mu metal); however, for particular applications, a quiteordinary iron sheet can suffice to achieve the desired shielding effect.

A cover 20 made of insulating material is mounted on top of the housing10. The cover 20 seals off the housing 10 with the current carryingconductors 12 so that they are protected from accidental contact.

The cover 20 is provided with pockets 22, which are likewise made ofinsulating material, in the region of the conductor loops 14. Thepockets 22 project downward from the cover 20 and are each situatedwithin the conductor loops 14 when the cover 20 is mounted. The pockets22 are open at the top at the level of the main plane of the cover 20,but are closed on all sides at the bottom in the region of the conductorloop 14. The width of each pocket 22 corresponds fairly accurately tothe limb spacing of the conductor loop 14, so that the outer sides ofthe pocket 22 are at only a short distance from the lateral limbs of theconductor loop 14, or else even bear against the latter. The depth ofthe pockets 22 is less than the depth of the conductor loop 14. Thelength of the pockets 22 (in the direction of the width of the conductorrail 12) can be greater, the same as or less than the width of theconductor rails 12.

Above the cover 20, there is a main circuit board 30. The main circuitboard 30 rests removably on the cover 20 with a small spacing.

Perpendicular to the main plane of the main circuit board 30, smallcircuit boards 40 are mounted on the main circuit board 30 and arearranged such that they extend into the pockets 22 of the cover 20 whenthe main circuit board 30 is mounted on the cover 20.

Hall sensors 42 are mounted on the small circuit boards 40. As FIG. 2shows, the Hall sensors 42 are fitted in indentations 43 approximatelyin the center of the bottom, free side or edge of the small circuitboards 40 such that the Hall sensors 42 are located centrally in thepockets 22 of the cover 20 and approximately centrally in the currentloops 14 when the circuit board 30, the cover 20 and the housing 10 areassembled. In this arrangement, the Hall sensors 42 are arranged suchthat the magnetic field of the current loop 14 permeates the Hallelement in the Hall sensors 42 perpendicularly. The main plane of theHall sensor 42 thus runs perpendicular to the main plane of the smallcircuit board 40. The indentation 43, matching the Hall sensor 42exactly, in the bottom of the circuit board 40 simplifies correctplacement of the Hall sensor 42 and ensures that the Hall sensor 42maintains its position.

In the immediate vicinity of the Hall sensor 42, the circuit board 40 isprovided with a temperature sensor 44, for example an NTC temperaturesensor. In addition, an amplifier 46 which amplifies the signal from theHall sensor 42 is located on the circuit board 40. The amplified signalsfrom the Hall sensor 42 and the signals from the temperature sensor 44are passed to the main circuit board 30 via conductor tracks 48.

The signals from the Hall sensors 42 and the signals from thetemperature sensors 44 are processed further on the main circuit board30. To this end, the necessary electrical and electronic components arearranged on the main circuit board 30, for example integrated circuits32, resistors, diodes, relays etc. (only some of which are shown in FIG.1). The main circuit board 30 preferably includes a microprocessor.

The signal from the temperature sensor 44 is used to provide temperaturecompensation for the signal from the Hall sensor 42. Since thetemperature sensor 44 is situated in the immediate vicinity of the Hallsensor 42, its temperature is recorded very accurately. Thetemperature-corrected signal from the Hall sensor 42 can be used todetermine the current flowing in the conductor 12 accurately.

Above the main circuit board 30 with the small circuit boards 40 thereis a covering 50. The front (the outer side) of the covering 50 has anLCD display 52, buttons 54 for entering commands, variables etc. andconnectors 56 for external connections. The covering 50 is electricallyconnected to the main circuit board 30 via internal connectors 34 on themain circuit board and/or via cables.

The buttons 54 can be used to set the microprocessor on the main circuitboard 30 to particular modes of operation using menu control. Thus, forexample, the LCD display can alternately show the currents in theindividual phase lines, the (total) power supplied and other variables,such as nominal and actual values. By specifying nominal values forcurrent and time, the current measuring device can also be used as aprotective circuit breaker, with turn-off commands and the like beingpicked up via the external connectors 56. The main circuit board 30 canalso contain relays and control terminals which condition and pass onthe switching signals.

FIG. 3 shows a block circuit diagram for the electronic components ofthe current measuring device. The schematic illustration in FIG. 3summarizes the processing of the signals from the Hall sensors 42 andthe temperature sensors 44, of the input signals from the buttons 54 andthe connector 56 and of the output signals to the LCD display 52, theconnector 56 etc. Signal processing is carried out not only on the maincircuit board 30, but also, in part, on the small circuit boards 40 withthe Hall sensors 42 and, if applicable, other components, not arrangedon the main circuit board 30, for example in the LCD display block 52 onthe covering 50.

As FIG. 3 shows, the current signals from the Hall sensors 42 and thetemperature sensor(s) 44 are amplified in amplifiers 61 and are passedto an A/D converter 62. From the A/D converter 62, the signals go on toa microprocessor 63. The input signals for the microprocessor 63 alsoinclude the “keyboard” signals supplied via a keyboard buffer 64. These“keyboard” signals are the control and monitoring signals which areinput externally using the buttons 54 and/or the connector 56, define inwhich mode the microprocessor 63 is intended to operate and which can beused, within the individual modes, to stipulate, by way of example,nominal values for the current, limit values and the like.

The programs which the microprocessor 63 uses to operate in theindividual operating modes are stored either in the microprocessor 63itself or in separate read only memories (not shown).

A power supply 65 supplies the electronic components with the necessarypower.

The input signals are processed in the microprocessor 63 on the basis ofthe respective mode of operation and on the basis of the respectivestipulations. Depending on the result of the processing and on the modeof operation, the microprocessor 63 then outputs control signals for theLCD display 52 to an LCD display controller 66, switching signals to arelay drive unit 67 and/or data of any type to an interface 68 forpassing on the data externally on a data bus, for example.

By way of example, if the current measuring device is in a motorprotective mode, the relay drive unit 67 can be used for directlyswitching relays (not shown) which interrupt the power supply to themotor under particular conditions (for example a high current over anexcessively long time). In addition, or as an alternative, an alarm canbe triggered, the excessively high current or the turning-off of acentral control location can be reported, and other such aspects.

What is claimed is:
 1. A current measuring device comprising: a currentcarrying conductor in an insulating housing; and a Hall sensor arrangedin the vicinity of the conductor, in which the current carryingconductor is a flat rail which is bent, in the region of the Hallsensor, into a U-shaped loop surrounded by a metallic shield againstmagnetic fields, and the Hall sensor is located on a circuit board whichis arranged in the U-shaped conductor loop, wherein the circuit boardwith the Hall sensor is fitted on a main circuit board on which thesignal from the Hall sensor is processed, and wherein an insulatingcover for the housing is arranged between the housing with the currentcarrying conductor and the main circuit board, said cover having aninsulating pocket which extends into the conductor loop and holds thecircuit board with the Hall sensor.
 2. The current measuring device asclaimed in claim 1, wherein a covering having a display of the currentflowing through the conductor is fitted above the main circuit board. 3.The current measuring device as claimed in claim 1, wherein, on the freeside of the circuit board extending into the conductor loop, there is anindentation into which the Hall sensor is inserted perpendicularly tothe main plane of the circuit board.
 4. The current measuring device asclaimed in claim 1, wherein a temperature sensor is fitted on thecircuit board in the immediate vicinity of the Hall sensor.
 5. A currentmeasuring device comprising: a current carrying conductor in aninsulating housing and a Hall sensor arranged in the vicinity of theconductor, the current carrying conductor being a flat rail which isbent into a U-shaped conductor loop; a main circuit board and aninsulating cover, wherein said main circuit board, said insulating coverand said insulating housing are configured to be assembled together,wherein the Hall sensor is carried by the main circuit board on whichthe signal from the Hall sensor is processed, said Hall sensor isarranged to extend into said U-shaped loop when said main circuit boardis assembled with said housing, and wherein said insulating cover forthe insulating housing includes a base portion arranged between theinsulating housing and the main circuit board, and an insulating pocketwhich extends from the base portion; and when said cover is assembledwith said housing, said pocket projects into the conductor loop and whensaid main circuit board is assembled with said housing said Hall sensorprojects into said pocket, said pocket surrounding the Hall sensor toinsulate said Hall sensor from said conductor loop.
 6. The currentmeasuring device as claimed in claim 5, wherein the Hall sensor isinsulated from the U-shaped conductor by the pocket without aninterposed ferromagnetic core between the Hall sensor and the conductorloop.
 7. The current measuring device as claimed in claim 5, whereinsaid Hall sensor is carried on a sensor circuit board which is fitted onthe main circuit board and extends perpendicularly thereto.